In recent years with the increase in oil prices and the increasing awareness of growing waste problems, there has been an increasing interest in the reclamation of usable waste materials from waste products. In recent years the process of pyrolysis has been used in reclaiming various materials from waste by providing a rapid decomposition and recovery of organic matter contained in the waste. Using this process on carbonaceous material such as plastic, wood, paper, cardboard, scrap rubber, coal, coke, coal tars, oils, live stock manure, and other garbage and solid waste will allow the reclamation of usable organic materials.
A major waste problem in the world today is the disposal of automobile and other vehicle tires. It is estimated that nationally two hundred million automobile tires and forty million truck tires are discarded annually in the United States alone. It is estimated that less than twenty percent of the tires removed from vehicles today are recovered for recapping for resale and only ten percent are reclaimed for other uses. The remaining seventy percent of the waste tires are a disposal problem.
In the past, tires have been burned or dumped in land fills in order to dispose of them. The burning of tires has long been disfavored due to the substantial amounts of noxious gases given off while burning. Tires are also undesirable for disposal in landfills since they do not readily deteriorate. In addition, scrap tires in landfills form an unhealthy breeding ground for insects, rats and other vermin.
In recent years there has been some success in recycling of tires and reclaiming usable hydrocarbons from scrap tires by use of pyrolysis. By the process of pyrolysis some tires have been advantageously processed to recover fuel and other hydrocarbon compounds. This fuel may be extracted in the form of highly aromatic oils and/or a gas which has heating values ranging from eighty to two thousand BTU per cubic foot. A by-product to this pyrolysis process is an ash or char material that remains after completion of the process. In the past this ash or char material was generally considered not worth salvaging unless it could be somehow reused as a filler or a low grade carbon black by industry, or if used as a fuel supplement to coal.
The industry has attempted to use this char as a low grade carbon black. This use has been found generally disadvantageous since the consistency of the char has been known to contain a random distribution of particle size from extremely small particles to extremely large particles. These particles range in size from less than one micron to over one thousand microns in size. This particulate matter, in its rough char form, is mixed with fiber and steel impurities from the tire or rubber feedstock which must be removed for use in industry and also consists of gritty sand like particles which are undesirable for use as a filler.
Such reclaimed char material has not generally been accepted in the industry due to the existence of these impurities and because of actual problems encountered in the industry by the use of such by-products as fillers or coloring agents in manufactured products. Although attempts have been made to filter out steel, fiber and ash, that remain in the char, by mechanical separation processes, these processes have generally not been sufficient to obtain a suitable product. Additionally, it has not been possible to filter out or separate the larger grittier particles from the desired carbon black particles by the present methods.
Therefore, the pyrolysis processes of the past have not generally been accepted in the industry as producing a sufficient grade carbon black, since the smallest particle size which has been obtained has been approximately an eighteen mesh (1,000 microns) char or carbon black product. The use of this unrefined product in materials as a carbon black has also found disrepute because products produced from these types of particles have been found to be less structurally stable than those same products produced with commercially produced carbon blacks. Therefore, it has been extremely difficult for those producing this char to find markets for the char by-product as a coloring additive, or carbon black filler.
Attempts have been made in the past to reduce the char particle size such that a more commercially acceptable grade of carbon black could be obtained. A fluid energy mill process has been used to pulverize the char particles to produce a finer particle size by way of implosion of all particles in the char material. Such a process is shown in U.S. Pat. No. 3,644,131 issued to Gotshall. These processes will produce in the one to ten micron range of char particles. However, the capital, expenditure and operating expenses for set up and operation, and the high amounts of energy cost required for use of such a process in production make the resulting product too expensive for normal scaled production. This process requires the grinding of all of the char material whether it is a desired carbon black or the undesired gritty type particle since it relies on reduction of all of the particle sizes no matter what the form is of the material contained in the char. This results in the grinding of some of the unwanted gritty material along with reduction in size of the carbon black material. Therefore this process has not been commercially exploitable at the present prices of carbon black due to the production costs involved and the impurities contained in the final product. The only potentially commercial application in which such a process could be exploited is in large scale facilities, such as a facility which could process approximately one hundred tons of tires per day. Thus, while tests run on the products using the material produced by this process seemed to have improved rubber reinforcing characteristics over the former unrefined char product, the cost and energy effectiveness of the process is extremely prohibitive.
In other attempts for refining the char material, a roller grinding mill similar to the type used to grind coal particles into fine particles for combustion etc. have been used in reducing the char particles. However, with this method the particle size is limited to about a 325 mesh or 45 micron bulk product. These 325 mesh char ground products have been used in formulations and did show improved rubber reinforcing properties, however, this process again has not been found to be commercially practical due to the excessive costs and high amounts of energy consumed by such a process to produce the desirable product. Again the process used is a size reduction process wherein all of the char material particle size is reduced. This causes some unwanted materials to be contained in the final product.
Therefore it has been a goal in the art to produce such a fine grade of carbon black without the expensive cost of production which were necessary in the prior art methods. There have been several attempts to produce a carbon black material which is suitable for industrial use and may be used exactly as its commercial counter parts but at a lesser cost which would make such a product truly feasible to produce, but up to the present time these attempts have been generally unsuccessful.
It has been known by persons using the unprocessed char that elastomeric/rubber formulas that use the unrefined char compound have substantially different properties than were expected. These compounds using the char were found to be less structurally stable than those using conventional carbon black. While these results were noted by others in the art, the reason for such a phenomenon was not pursued. The present inventor then took it upon himself to find out the cause of this problem when a char material was used in an elastomer/rubber formulation. Through extensive research and analysis of the chemistry, structure, and physical properties of the compounded rubber and the char particles from various char samples, it was discovered that large portions of the char materials that remain from the pyrolysis of carbonaceous material are actually agglomerations or clusters of small and even submicron carbon black and filler particles. It was also found that the char material also contained hard gritty unitary particles which are undesirable in a usable carbon black material. It was found that the agglomerations or cluster particles contain the sought after carbon black particles and that the hard gritty unitary particulate material is undesirable in a carbon black material.
Thus, the present inventor discovered that these char particles which were previously thought of and accepted as hard gritty unitary particles, which made it necessary to expend large amounts of energy to grind or mill the unitary particles to a smaller size, where actually a mixture of the hard gritty unitary particles and the agglomerate or cluster particles of many small carbon black and filler particles originally used in the material when it was compounded. The inventor has discovered that it is necessary to expend only enough energy to de-agglomerate the agglomerate or cluster particles to produce a quality carbon black material and leave the unitary particles intact.
Therefore, in using this discovery in a commercial application the inventor has discovered a new useful process for reclaiming a usable carbon black particulate material from discarded rubber by selective de-agglomeration of these cluster or agglomerate particles and the separation of the carbon black from the remaining gritty unitary particles. This process is commercially practical and requires less energy to be expended, thus resulting in a commercially practical use of this char material.